Limaflo MotoMouth Eurorack Module - DIY Build

Completed MotoMouth Module Front View

As the summer is ticks along, we decided to take on a relatively new module. The LimaFlo MotoMouth Formant Filter. MotoMouth was originally a Kickstarter project that was first launched in March of 2017, and thanks to its backers, the MotoMouth was born. Our buddies over at Synthrotek were one of the first to have the DIY kits and you better believe we had to get our hands on this one and line it up for our final July build. 

Before we get into the build notes, videos and audio samples, you are probably wondering what in the world that the MotoMouth does. The Motomouth is described as an analogue 3-Band, Sedra + Espinoza Bandpass Filter (DABP) with resonant frequencies that are tuned to the same resonant frequencies that are found in the human mouth and nose cavities.

These frequencies can be varied, independently, to form different ‘mouth shapes’, to emulate vowels such as A, E, I, O and U.  In the end, this module can essentially emulate 16 vowels and ‘morph’ or ‘glide’ between each vowel using a single Control Voltage input (1V/Oct), and a Gate to ‘snap’ to each vowel when required. 

LimaFlo Logo

So how does this all work? Well, we have to look at what and how formant filters work. To break it down, formant filters are different from lowpass (LP), highpass (HP) and bandpass (BP) filters in that they are comprised of at least 2 bandpass filters (F1 and F2) with very narrow bandwidths (generally fixed at around 60 to 100 Hz). F1 and F2 are moved to different resonant frequencies to mimic the resonance changes in the ‘mouth cavity’ when forming the different vowels. A third bandpass filter (F3) is preferably added to introduce the ‘nasal chamber’, but it’s generally kept static and makes little impact “in the mix”.

Is there any more to this? Yes… there is. Control Voltage is decoded to control F1 and F2 independently, because the frequency bands for each vowel are not proportional to each other over the vowel range.  The Limaflo Motomouth has virtually learned how to ‘speak’, so to speak, but it still needs to learn more, and that’s were the modular magic happens.

Enough with the technical jargon though, let’s get onto the build notes and the fun stuff!

Time Lapse and Build Notes

Play Video

MotoMouth is considered an intermediate to advanced hole-through build. Meaning, it is probably a good idea to have a few other builds under your belt before taking this one one. The main reason for this is dual PCBs and some rather tight soldering pads. You have to be precise with this one and if you get in a rush or you get sloppy with your solder, you would end up trying to track down some weirdness. 

If you struggle at reading BOMs (bill of materials), you might also want to get some practice in as well. While the BOM is clear, one could find themselves losing their place when going from one PCB to another while referencing the BOM throughout. Limaflo also does a great job providing a manual for the module, which makes things easier to understand. 

We definitely recommend checking things off the BOM as you go to help keep track of where you are and if you come back another day to continue the build.  Both Synthrotek and LimaFlo provide assembly instructions which can easily be referenced if you need to. A smart tool to have during this build is a capacitor/resistor tester. Since you will be handling a lot of these, this handy tool helps ensure you have the right value for the pad needed. 

As you advance through the build, keep a clean iron and don’t forget about your handy FLUX. This stuff can come in really handy if you are having issues with the solder not sticking to the board. (You will want to be sure to clean off the FLUX when you are done though). 

Upon finishing the build, we plugged the module into our test case and fired it up. Our sound was low and there was little we could do to get anything out of it. Here is the most important step to this entire build… calibration. While you can either us a multimeter or an oscilloscope, we recommend having a friend around to help. Just follow the calibration instructions carefully and you will be well on your way to experiencing this wild module.

MotoMouth Audio Demo

How does it sound? Well, once we got everything calibrated, we pushed several other modules through it (see audio sample video). Its VCF was throaty and it was able to handle anything we pushed through it. As for the “vowels” .. well that was cool. It felt like we were playing with a pissed off Speak and Spell.  (Ok … not that angry).  One thing is for sure…. we know that we will be using this formant filter in several of our patches and look forward to connecting it to our MIDI keyboard to control the gate of the module. 

Features and Specifications

Key Features::

  •  Single CV to control and set vowel shapes.
  •  Automatic Morphing and morphing rates to each vowel.
  • Pure analogue single path from input to output.
  • Gate operated snap to each vowel when required.
  • Sedra+Espinoza Analogue Filter design for a high, sharp Q value and a 12 dB/octave roll-off slope.
  • Plays well from a monophonic keyboard or Midi Keyboard through a Midi to CV/Gate converter.
  • Works great with a CV Step Sequencer.
  • Filter and vowel mode selection using the same single CV input.

Power and Specs:


           – Module width: 12HP

           – Module depth: 42mm

         Power draw:

             +12V: 80mA

             -12V: 4mA

Purchasing Information

PCBs, Panel and ICs

  • Black or Aluminum Panel
  • Multiple PCBs and ICs included
  • List Price: $49.99 USD
  • Click on the image to be redirected to the Synthrotek Store Page

MotoMouth DIY Kit 

  • Includes all components, PCBs and Panel for assembly
  • Black or Aluminum Panel
  • List Price: $149.99 USD
  • Click on image to be redirected to the Synthrotek Store Page

Assembled EVENT Module

  • Fully assembled and calibrated 
  • Black or Aluminum Panel
  • List Price: $115.00 USD
  • Click on image to be redirected to the Synthrotek Store Page

Limaflo MotoMouth - The Final Word

Overall Rating:

Design – 4 stars – the matte black is sleek and there is also an optional aluminum silver panel.  It would be nice to see some more color on the panel than the standard black/white combos. Nice knobs and bright LEDs give the module some depth of design.  

Calibration Procedures: 4 stars, somewhat difficult to understand, but having a buddy help you out makes it a lot easier. 

Usability: 4.5 stars – this thing is capable of a lot and we have only scratched the surface of its patchibility. We need more time with it. 

The LimaFlo Motomouth was a fun intermediate build that requires patience and attention to detail. Calibration can be confusing, but partnering with a friend to help hold the module helps a lot. The design is beautiful but could use a little more color on the panel. Motomouth’s uniqueness and its reasonable price options, make for an affordable filter for any rack. Hands down…. this module will add some flare and some new capabilities to your rack that you will want to use over and over. 

Until the next build … 

~ f i N

Completed MotoMouth Module Front View